Vacuum work holder



Aug 3, 194 I g MQRRI$QN 2 6 293 VACUUM WORK HOLDER Filed 001;. 18, 1947 INVENTOR CLIFFORD MORRISON ATTORNEYS Patented Aug. 3,1948

VACUUM WORK HOLDER Clifford Morrison, Los Angeles, Calif assignor to Western Equipment Company, a copartnership composed of Oliver 1!. Calhoun and Adela 11. Calhoun Application October 18, 1947, Serial No. 780,729

9 Claims. I

This invention relates generally to work holders or chucks wherein the work is retained against a surface of the work holder by means of a vacuum. The invention disclosed herein represents an improvement upon the invention dis closed in the copending application for patent of Clifford Morrison and Joseph F. Hoch, Serial No. 622,200, filed October 13, 1945, and now Patent No. 2,443,987, granted June 22, 1948.

It is now becoming the practice to machine sheet stock of aluminum to form thin tapered sheets or skins adapted to be incorporated as integral parts of the wings and fuselage ofairplanes. The tapered sheets must necessarily be machined to thin sections and the work held to close tolerances. Heretofore great difliculty has been experienced in securely holding the individual sheet in a flat plane while the sheet is being machined to a thin tapered section. In order to hold the sheet securely, it is necessary to adequately support the undersurface of the sheet throughout its entire area in a common plane and at the same time adequately hold the sheet throughout its entire area so that the same cannot buckle or draw away from the plane in any local area.

It therefore is an object of this invention to provide a novel means for securely holding a thin sheet, such as a sheet or plate of aluminum, in a plane while the sheet is being surface machined to produce a thin tapered sheet or skin of the type indicated.

It is also an object to provide a means for supporting the sheet in which maximum support is given to the undersurface of the sheet and at the same time substantially the entire under surface of the sheet is subjected to a vacuum effected between the work holder and the sheet.

It is a particular object to provide a vacuum type work holder provided with a novel, efficient work holding surface which adequately supports It is also a particular object of this invention to provide. in a vacuum work holder of the type indicated having means for effecting a seal between the work and the holder, a new andimproved apparatus and method for evacuating air from between the work and holder which serves to prevent leakage of air across the work holder- 2 between it and the work in the event of a. failure of the seal and consequent leakage of air therethrough.

These and other objects and advantages will be apparent from the drawing and the following description. Referring to the drawing:

Fig. 1 is a plan view of a work holder embodying the invention;

Fig. 2 is an enlarged fragmentary plan view of a corner portion of the work holder in which the surface channeling has been schematically indicated by single lines;

Fig. 3 is a section on line 3-3 of Fig. .2;

Fig. 4 is an enlarged cross section of the surface channeling; and

Fig. 5 is a section similar to Fig. 4, showing a modified form of surface.

More particularly describing the invention. reference numeral ii generally indicates a vacuum type work holder or chuck of a type designed for supporting flat sheet stock and the like to be machined. This work holder includes, generally, a work holding surface 12 which is bounded at the margins of the holder by a gasket groove or channel M in which is positioned a suitable gasket i5 for effecting a seal between the Work holder and-a work piece placed thereon. Reference is made to the copending application of Clifford Morrison and Harold F.-Dumbleton, Serial No. 780,730, filed Oct. 18, 1947, for a more complete disclosure of a suitable type of construction for providing a seal between the work and the work holder by means of a groove and a gasket construction.

As previously indicated, it is desirable to support the work over as great an area of its undersurface as possible and at the same time be able to subject substantially the entire undersurface of the work 'to a vacuum. If local areas or spots of any extent are unsupported, the sheet or work piece may be depressed or low in such spots during machining. On the other hand, if a sheet is not securely held down throughout it will rise in local areas when it is machined. In either case, this causes uneven and unsatisfactory machining of the work. a

Preferably, these channels are extremely small in g size, that is, they need be only barely large enough to pass air to permit the air to be exhausted therefrom.

The channels communicate with each other or 3 intersect and also communicate with the gasket groove or channel l4 bordering the general work holding surface l2. One convenient way of forming the channels I! is by utilizing a rotary fly cutter having a cutting tool of the desired dimensions and either moving the cutter over the work holder or feeding the work holder to the cutter. By feeding the work holder longitudinally at a rate of approximately one-half inch per minute and rotating the fly cutter at a speed of about one hundred R. P. M., a. surface is produced which is characterized by a series of substantially circular intersecting channels I! which define lands 20 (Fi 4).

In forming the work holding surface, I prefer to pass the cutter back and forth (or feed the work back and forth) over the surface l2 of the work holder to produce a plurality of rows 2! of the grooves or channels it. The rows should overlap each other and the cutter should be passed over the wall portion 24 defining the outer side of the gasket groove to insure the upper surface l2 of said wall portion 24 being in the same plane as'the surface I2 and to insure the grooves or channels I8 communicating with the gasket groove M. This method provides a surface which adequately supports the work, yet enables the subjection of substantially the entire undersurface of the work to a vacuum. By having, the channels l8 extend outwardly from the gasket groove I through the outer edge of the surface [2, the under side of the top or flap portion of the gasket I is placed in communication with atmosphere, thus facilitating the flap portion of the gasket being drawn into'sealing engagement with a sheet in response to exhausting air from the channels. 1

I In order to evacuate air from between a work piece resting on the work holder and the holder, I provide a plurality of bores or exhaust ports 25 in the work holder which communicate with tubes 26 connected to a main air exhaust pipe 28 leading to a suitable means for exhausting air (not shown). Preferably the bores are located close to the gasket groove 14, and, to insure rapid evacuation of air from the groove inwardly of the seal formed by the gasket, exhaust grooves or channels 29 are provided between the gasket groove and each bore 25. By exhausting air near or at the gasket groove, and hence at the margins of a work piece on the holder, I not only rapidly initially evacuate air from between the work and the holder, but I provide a means of immediately exhausting any air which may leak past the gasket and thus prevent such air from working under or having to pass under the work piece before it is exhausted with the consequent danger of the loosening of the work piece while being machined. As will be noted in Figs. 1-3, the grooves 29 are each of a depth or cross-sectional area greater than that of each of the channels l8.

In the operation of the device, a work piece of suflicicnt size to extend .over the gasket I5 is placed on the work holder and air exhausted through ports 25. As air is exhausted the gasket forms a seal against the work piece. The intercommunicating channels N3 of the surface l2 serve to provide an adequate system of passages for the escape of air from under the work piece to the exhaust ports, while the lands 20 provide adequate support for the work.

In Fig. 5 there is shown a modified form of surface, indicated by l2a, which differs from that previously described in that the lands 20a defined by the channels I 8 are flattened in a common plane. This can be accomplished by sanding, grinding or milling the surface I! previously described. This surface gives more support to the work and might be usefully employed where extremely thin sheets are to be machined.

Although the invention has been particularly shown and described, it is contemplated that various changes and modifications may be made without departing from the scope of the invention as set forth in the following claims.

I claim:

1. A vacuum sheet stock holder comprising a body having a surface presenting a continuous marginal groove, that portion of the surface surrounded by the groove presenting a plurality of sheet-engaging lands separated by intervening depressions defining air passageways communicating with the groove, and a continuous flexible gasket mounted in the groove, said body having an air-exhausting port and a channel forming an extension of said port, the channel being of greater cross-sectional area than the individual passageways and intersecting and communicating directly with. the groove at a point inwardly of the gasket whereby to exhaust air from the groove I and from the passageways through the groove.

2. A vacuum sheet stock holder comprising a body having a surface presenting a continuous marginal groove, that portion of the surface sur rounded by the groove presenting a plurality of sheet-engaging lands separated by intervening depressions defining air passageways communieating with the groove, and a continuous flexible gasket mounted in the groove, said body having an air-exhausting port and a channel forming an extension of said port, the channel being deeper than said passageways and intersecting and communicating directly with the groove at a point inwardly of the gasket whereby to exhaust air from the groove and from the passageways through the groove.

3. A vacuum sheet stock holder comprising a body having a surface presenting a continuous marginal groove, that portion of the surface sur rounded by the groove presenting a plurality of sheet-engaging lands separated by intervening depressions defining intercommunicating air passageways communicating with the groove, and a continuous flexible gasket mounted in the groove, said body having an air-exhausting port and a channel forming'an extension of said port, the channel being of greater cross-sectional area than the individual passageways and intersecting and communicating directly with the groove at a point inwardly of the gasket whereby to exhaust air from the groove and from the passageways through the groove.

4. A vacuum sheet stock holder comprising a body having a surface presenting a continuous marginal groove, that portion of the surface surrounded by the groove presenting a plurality of sheet-engaging lands separated by intervening depressions defining intercommunicating air passageways communicating with the groove, and a continuous flexible gasket mounted in the groove, said body having an air-exhausting port and a channel forming an extension of said port, the channel being deeper than said passageways and intersecting and communicating directly with the groove at a point inwardly of the gasket whereby to exhaust air from the groove and from the passageways through the groove.

5. A vacuum sheet stock holder comprising a body having a surface presenting a continuous marginal groove, that portion of the surface surtersecting the groove.

6. A vacuum sheet stock holder comprising a body having a surface, presenting a continuous, relatively deep marginal groove, that portion of the surface surrounded by the groove presenting a plurality of coplanar sheet-engaging lands separated by intervening relatively shallow depressions defining air passageways intersecting the groove, and a continuous flexible gasket mounted in the groove, the gasket having a base portion disposed in the bottom portion of the-groove and a flap portion disposed upwardly and outwardly, out of sealing engagement with the air passageways, to a point above the plane of the lands, said body having an air-exhausting channel, of greater cross-sectional area than the individual passageways intersecting the inner side wall of the groove at the top thereof.

7. A vacuum sheet stock holder comprising a body having a surface presenting a continuous marginal groove, that portion of the surface surrounded by the groove presenting a work-engaging area, and a continuous gasket having a base portion mounted in the bottom portion of the groove and a flexible flap portion adjoining the top of the base portion below the plane of the top edge of the inner side wall of the groove and extending upwardly and outwardly therefrom, the body having an air-exhausting channel intersecting the inner side wall of and communicating with the groove at a point above the base portion of the gasket and having an air passageway communicating at one end with atmosphere and communicating at its other end with the groove through the outer side wall thereof, whereby to expose the under surface of the flap portion to atmosphere when the top surface of said flap portion is exposed to vacuum resulting from exhaustion of air through said channel.

8. A vacuum sheet stock holder comprising a body having a surface presenting a continuous marginal groove, that portion of the surface surrounded by the groove presenting a work-engaging area, a continuous gasket having a base portion mounted in the bottom portion of the groove and a flexible flap portion adjoining the base portion below the plane of the top edge of the inner side wall'of the groove and extending upwardly and outwardly therefrom,-the body having an air-exhausting channel intersecting the inner side wall of and communicating with the groove at a point above the base portion of the gasket and having an air passageway communicating at one end with atmosphere and communicating at its other end with the groove through the outer side wall thereof, whereby to expose the under surface of the flap portion to atmosphere when the top surface of said flap portion is exposed to vacuum resulting from exhaustion of air through said channel, and a plurality of depressions within said work-engaging area defining air passageways intersecting the inner side wall of the groove adjacent the point at which said flap portion adjoins the base portion of the gasket.

9. A vacuum sheet stock holder comprising a body having a surface presenting a continuous marginal groove, that portion of the surface surrounded by the groove presenting a work-engaging area, and a continuous gasket having a base portion mounted in the bottom portion of the groove and a flexible flap portion adjoining the base portion below the plane of the top edge of the inner side wall of the groove and extending upwardly and outwardly therefrom, the body having an air-exhausting channel intersecting the innerside wall of and communicating with the groove at a point above the base portion of the gasket.

. CIIFFORD MORRISON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,366,005 Jansson Jan. 18. 1921 2,400,314 Obency May 14, 1046 

